The present invention relates to an apparatus for the automatic, vertical stacking of sheets.
A stacking apparatus of this type has already become known to the applicant from U.S. Pat. No. 4,772,169. In this prior publication, on one side of the compartment for forming the stack, to be more precise in the region of the upper stop of the fork for forming the stacks, there is provided a fixedly arranged apparatus for feeding the lower cover board and the upper cover board for the stack. On the other side of the compartment for forming the stacks consisting of sheets there is provided a station for compressing and tying up the stacks. For conveying away the finished stack, out of the compartment into the pressing and tying apparatus, there is provided a carriage-like device, which is provided with vertically arranged side parts which form limiting bars which bear against the sides of the stack of sheets.
It is known that, for reasons of safety, in automatic, vertically arranged stacking apparatuses the cycle for conveying away the stack of sheets is longer than the cycle for conveying away the bundles in vertical, manually operated stacking apparatuses.
In the case of automatic stacking apparatuses, the lower cover board is placed on the fork when the latter has reached its upper position, to be precise after stopping the fork in its upper end position. Since the finished stack is also temporarily stopped in the downward movement in order to permit the upper cover board to be placed on, for reasons of safety there are in automatic stacking apparatuses additional waiting times of the order of 4 to 5 seconds per cycle. These delays do not occur in the case of stacking apparatuses to be loaded manually. Therefore, a time saving of the order of 20 to 30% is achieved for the operation of conveying away the stacks. In the manually loaded stacking apparatuses, the operator usually places the lower cover board on the fork already during its upward movement and the upper cover board is placed on the finished stack of sheets after setting the stack down on the roller conveyor. In other words, the operator uses one hand to place the upper cover board on the stack and the other hand to begin already moving this stack in the direction of the pressing and tying apparatus.
It is furthermore known that attempts have been made to increase the efficiency of rotary printing machines which are arranged upstream of the stacking apparatuses described. This increase in performance is measured in sheets per hour.
An increase in the performance of automatically operating, vertically arranged stacking apparatuses could be achieved by faster conveying away of the stacks of sheets or by increasing the prestacking stroke, which is defined by the upper position of the pivotable blade and the upper position of the fork. Due to safety periods which have to be observed, there are very confined limits within which the operation of conveying away the stack of sheets can be shortened. An increase in the prestacking stroke would result in an increase in the overall height of the stacking apparatus. If it is borne in mind that, in the case of the known stacking apparatuses for stacks having a stack height of 1 m, the stacking apparatuses can still be directly accessed and operated in order to carry out monitoring and maintenance work, it is obvious to a person skilled in the art that an increase in the overall height of the stacking apparatuses by, for example, 20 to 40 cm on account of an increase in the prestacking stroke is not acceptable in practice for various reasons. Stacking apparatuses of such increased overall height would require the use of steps, stools, stairs, handrails, balcony-like adjoining structures and safety equipment. These additional items require a larger installation area. This disadvantage is particularly serious if a series of stacking apparatuses are provided alongside one another.
It must also be taken into consideration that, with an increase in the prestacking stroke, the possibility of producing less high bundles is correspondingly restricted.